Method and device for draining submerged tanks

ABSTRACT

A device for draining fluids from a submerged tank, including a flexible pipe which can be submerged from a loading craft, this pipe being associated with at least one line for transmitting power from the loading craft, and being provided, substantially at its lower end, with means for connection to a coupling element on the submerged tank and with suction and delivery means, actuated by the power transmitted by the power line from the loading craft.

United States Patent [72] Inventors Jacqaealiarbonn Jouars Pontchartrain; Jacques Garnier, Le Cliesnay, both of, France [21] Appl. No. 829,596

[22] Filed June 2, 1969 [45] Patented June 8, 1971 [73] Assignee lnstitut Fraucais du Petrole des Carburants et Lubriflants Ruell Malmalson (Hauts de Seine), France [54] METHOD AND DEVICE FOR DRAINING SUBMERGED TANKS 13 Claims, 4 Drawlng Figs.

325/29, 340/3 [51] lnt.Cl. B67c 3/02 [50] FieldofSearch 14l/1,94, 192, 284, 346-350, 382, 387, 388; 103/87 E, 102; ll4/0.5 T; 61/723; 325/25, 28, 29, 66,116;

[56] References Cited UNITED STATES PATENTS 2,901,889 9/1959 Reed 103/98(E) 3,222,634 12/1965 Foster 340/3 Primary Examiner-Houston S. Bell Jr. Attorney-Craig, Antonelli, Stewart and Hill ABSTRACT: A device for draining fluids from a submerged tank, including a flexible pipe which can be submerged from a loading craft, this pipe being associated with at least one line for transmitting power from the loading craft, and being provided, substantially at its lower end, with means for connection to a coupling element on the submerged tank and with suction and delivery means, actuated by the power transmitted by the power line from the loading craft.

1 3 1 INVENTORS' rAcauEs HAKBONN and Ac uE; GARNIFIQ 1 $20M q M ATTORNEYS PATENIEU JUN 8I97l 3,583 3145 saw 2 or 3 m qes HAKBONN and JMQMSGARNM B2417, M Q

ATTORNEYS m 0 5 m 4 W 3 8 3 ,r 3 M (n m 3 M M J 1 .r -8 A m M S PATENTEB Jun 8 l97| JACGHES HARBONN and JAGQUES GARNIER 4 417 XMMy/ J v 3/41 ATTORNEY 3 METHOD AND DEVICEFOR DRAlNlNG SUBMERGED TANKS The companies possessing licenses for oil prospecting and producing in deep water or at great distance from the coasts are contemplating the installation of underwater tanks for collection of degasified crude oil.

These tanks would be supplied with crude oil from submerged oil well heads, or with degasifled crude oil from degassing units connected to the well heads, through pumping means capable of filling up the tanks under a pressure which substantially balances the hydrostatic pressure applied to the external wall of the tanks.

It may be contemplated to carry out the draining of these underwater tanks through pipes connecting the tanks to a surface installation, such as a buoy or a loading platform, to which tankers could moor.

Such a permanent installation would however be expensive and dangerous to shipping, while being moreover subjected to all the effects of wind and waves at the water surface.

Alternatively the pipes might be connected to a pumping station located at some depth so as to be withdrawn from the influence of waves and winds and not interfere with naviga tion, while being within the reach of divers, so as to make it possible to connect draining pipes to this pumping station from an oil tanker.

This second solution is also expensive and, as the first one, requires the use of pumps capable of draining the hydrocarbons from the depth at which the tanks are submerged, which limits the depth of immersion of these tanks as a result of the increase in the pressure drop through the draining pipe as the depth becomes greater.

As a matter of fact, even if it is contemplated to lift to the water surface the oil contained in the tanks by employing the hydrostatic pressure of the surrounding water and taking ad'- vantage of the difference in the respective specific gravities of water and oil, by constituting for example at least one of the walls of each tank of a flexible material or by using tanks having a mobile wall or also by letting the surrounding water penetrate into the tanks so as to displace the oil therefrom, the use of draining pumps would be necessary in both the hereinabove indicated solutions, when it is desired to drain the fluid at a higher flow rate than that resulting from the sole action of hydrostatic pressure.

Moreover the utilization of draining pumps would result in the risk of the pump frequently running dry as a result of cavitation phenomena when there is drained crude oil, which is a mixture of gas and liquid.

it is also possible to equip the tanks with delivery pumps, but such a solution would being the problem of supplying power to these pumps and of repairing or replacing them when the tanks are located at great depths.

The main object of the invention is accordingly to provide a more simple method for draining underwater tanks and a device for carrying it out, which eliminate the need for a network of submerged draining pipes and consequently the need for valves and automatic safety devices in such a network for delivery pumps submerged with the tanks and loading buoys or platforms.

Another object of the invention is to provide a draining device whereof all the essential elements can be raised to the water surface, thereby facilitating their servicing.

These objects are achieved according to the invention with a device for draining to a loading installation, which may be located on the water surface, fluids contained in at least one submerged tank, this device including at least a flexible pipe which can be submerged from the loading installation, said pipe being associated to at least one line transmitting power from the loading installation said line being provided at its submerged end with means for connection to a coupling element of said tank and with means for draining and delivering the fluids, actuated by said power transmitted through said power line. This power line may either be an electric power line, in the case where said draining and delivering means is constituted by an electric pump, or by an hydraulic power line, in the case where the engine driving the pump is hydraulie.

One of the essential advantages of using a suction and delivery pump located substantially at the submerged end of the flexible pipe, results from the fact that the pump being then permanently in contact with the fluid in the tank, this fluid can be drained without any substantial pressure drop due to the suction and any risk of the pump running dry, while making it possible to continuously provide for a sufficient flow rate.

Moreover, in the case of a plurality of tanks, the device according to the invention exhibits the economically very substantial advantage of requiring only one pump for draining several tanks, whereas this result could only be achieved by having a number of pumps equal to the number of tanks when using pumps associated to the tanks.

An additional object of the invention is to provide a method for draining a submerged tank which belongs to a set of such tanks from a mobile installation or craft equipped with a dynamic anchoring device provided with means for determining the position of said installation with respect to a system of beaconing or ranging units.

In an embodiment of the invention, the meansfor connecting the pipe with a submerged tank cooperates with a drawoff valve provided with a floating piston and located at the top of the tank, this valve being adapted to receive the lower end of the pipe and to establish a communication between the latter and the inside of the tank by downward displacement of said floating piston.

The drawoff valve equipping each underwater tank will not however necessarily be of the floating piston type, any other suitable type being also applicable, in particular singleele ment valves or valves provided with overlapping elements, hinged diaphragms or moving jaws, all these devices being so designed as to provide for sealing during lowering of the equipment and for automatic full closure after withdrawal of said equipment.

The lower end of the pipe will advantageously be provided with a device for transmitting and receiving acoustic signals for location of its position, this device including means for transmitting a narrow ultrasonic beam rotating around the axis of the lower end of the pipe and cooperating with at least three ultrasonic reflectors or responders secured to the upper part of each tank, around the draining valve.

The term acoustic signals" is used here with a very broad meaning, covering not only the waves transmitted within the range of the audible frequencies, but also ultrasonic and subsonic vibrations, as well as shock waves and those generated by vibrations in water.

The location of the position of the ship with respect to" the underwater tank will preferably be performed in the manner described in U.S. Pat. No. 3,421,138. Using at least three beaconing or ranging units of the type specified in this patent, each of which including a hydrophone electrically connected to a buoy provided with a surface radio transmitter, the hydrophones of these beaconing units having fixed locations with respect to the seabed,- in the vicinity of the underwater tank or tanks.

A nonlimitative embodiment of the invention is described herein under with reference to the attached drawings wherein:

FIG. 1 illustrates an overall view of this embodiment,

FIG. 2 shows on a larger scale the lower end of the drawing pipe and FIG. 2A shows the device for guiding this lower end to the valve of the tank to which the pipe is to be connected,

FIG. 3 diagrammatically illustrates the device for guiding the lower end ofthe pipe, by means of ultrasonic waves.

FIG. 1 shows, by way of example, a set of six tanks for deg'asified crude oil (tanks 1 to 6), supplied through the pipes 7 to 12 respectively, from submerged oil wells,- through degassing devices which have notbeen illustrated.

Each of these tanks, as shown for the tank 1, has its top equipped with a drawoff valve l3-which, in this embodiment,

is of the floating piston type, the lowering of the piston permitting withdrawal of the oil. However such a type of valve is not limitative, no more than the arrangement of the valve at the top of the tank.

A loading tanker 14 is positioned substantially in plumb with the underwater tank from which crude oil is to be drained.

The position of the ship 14 is maintained throughout the draining operation by means of a dynamic positioning system of any appropriate type.

For example, this system may include two directionally controllable propulsion units 15 and 16, the thrusts of which are opposed to the action of external forces tending to displace the ship from the selected position.

The dynamic positioning system may have manual or preferably fully automatic control.

This system will comprise means for locating the position of the ship, which will preferably be constituted as specified in the patent quoted hereinabove.

In the embodiment illustrated in FIG. 1, four beaconing or ranging units of the type described in the prior patent are employed, this number being by no way limitative.

Each of these units comprises a hydrophone or receiver for acoustic signals, located in a fixed position on the seabed or in close vicinity thereto, being for example incorporated in a mooring block.

The four hydrophones H,, H,, H and H, are for example located at the apexes of a square forming a system of reference for the respective positions of the different underwater tanks 1 to 6.

The different hydrophones are connected by means of cables l7, l8, l9 and to surface buoys B,, 8,, B and B of which each is provided with a radio transmitter electrically connected to the corresponding hydrophone and transmitting in accordance with a code characteristic of this hydrophone (for example on a frequency characteristic of this hydrophone).

Acoustic interrogation signals, for example ultrasonic signals, are transmitted into the water from a transmitter 21 beneath the ship and their reception by the different hydrophones controls the radio transmission, from the buoys B,, 8,, B, and B of response signals corresponding respectively to these different hydrophones, which are intercepted by the aerial 22 on the ship, making it possible to determine the position of the ship 14 with respect to the vertical passing through the location of the considered tank, by means of the coordinates of this ship in the reference system formed by the beaconing units (11,, 8,; H,B,; H,B,; H 8

The position of the ship can be corrected, if necessary, as specified in the above-indicated patent.

The ship 14 being maintained substantially in plumb with the selected tank, by means of the dynamic positioning system, a flexible pipe 23, for example stored on a reel 24 and connected in known manner to collecting tanks (not illustrated) by means of a rotary joint fitted to the shaft of the reel, is unreeled from the ship.

in its lower portion, this pipe is provided with a suction and delivery pump 25 which can be inserted into the drawoff valve 13 to allow draining of the underwater tank.

The motor driving this pump is supplied with electrical power by means of conductors which may be incorporated in the pipe 23.

It will also be possible to use other forms of energy to drive the pump 25, for example hydraulic energy.

FIG. 2 shows on a large scale the lower end of the flexible pipe 23 and FIG. 2A the submerged tank 1, partially broken away.

This tank is provided at its top with a draining valve which, in this embodiment, is equipped with a floating piston 26 slidably mounted in a vertical tube and which is normally applied in sealed manner against an annular shoulder 28 at the upper end of this tube, under the action of the degasified crude oil fed into the tank through the pipe 7.

The tube 27 is provided with apertures 29 through which the pump 25 can drain the oil, when the lower portion of the pipe 23 is inserted into the pipe 27, thereby pushing back the piston 26 below the apertures 29 and allowing oil to be drawn off through the strainer 30 of the pump 25. In order to prevent the penetration of sea water into the tank, the piston 26 of the valve, which slides in the tube 27 with a small clearance which provides for sealing, is normally impelled into a position located at a level above the apertures 29, irrespective of the level of liquid in the tank, by means of return devices (not shown) exerting an upward force on the piston 26, the magnitude of this force being substantially greater than the hydrostatic pressure acting on the piston.

One or more packing elements 27a, located close to the lower end of the pipe 23 and/or within the tube 27, cooperate with the internal wall of the tube 27 and/or with that of the annular shoulder 28, to ensure the sealing of the tank in this draining position. The packing element 270 will for example be inflated through the duct 23 when it is positioned within the tube 27.

The insertion of the lower end of the pipe 23 into the tube 27 may optionally be facilitated by using a guide cone 31 located at the top of the floating piston valve 13.

This insertion will be performed by combining the dynamic anchoring of the loading ship 14, in plumb with the tank, with a precise guiding of the lower end of the pipe 23, associating propulsion means adapted to said lower end with means for very precise determination of the position of this lower end relative to the upper orifice of the valve 13.

This propulsion means may, for example, consist of one or more jets of fluid under pressure.

For these jets, at least four orifices 32, 33, 34, 35 will for example be employed, preferably located in two planes at right angles passing through the axis of the pipe 23, as illustrated, in order to adjust the resulting thrust exerted by the jets on the lower end of the pipe 23, by means of two components of this resulting thrust, at right angles to each other, in the two possible directions.

The liquid generating the jets will for example be water pumped under pressure by one or more pumps which may be submerged or located at the surface, into the pipe 23, and the force of each jet will be adjusted by the greater or lesser opening of a control valve or slide valve associated with each orifice, for example through electrical remote control conductors which the opening of these slide valves being controlled from the surface may be incorporated in the pipe 23. The apertures 32 to 35 are closed during the draining operation of the pump 25.

The propulsion means at the lower end of the pipe 23 may also be constituted by propulsion units actuated by electric motor supplied with current from the surface through conductors incorporated in the pipe 23.

The means for accurately locating the position of the lower end of the pipe 23 may also consist of a television camera or preferably many cameras, associated with projectors and transmitting a picture of the upper end of the tank to the ship 14 through conductors incorporated in the pipe 23.

However a device for precise location using acoustic signal, of the type specified herein under, will be preferably used, since this device makes it possible to ascertain at any moment the position of the lower end of the pipe 23 from the respective distances between this lower end and at least three fixed reference points of the top of the tank, which makes it possible to have a fully automatic control of the four jets at 32, 33, 34, and 35 by using a feedback control system of a type well known to those skilled in the art.

An embodiment of a device for precise location by means of ultrasonic signals, applicable for this purpose, is described hereinafter with more particular reference to FIGS. 2 and 3.

This device includes an ultrasonic transmitter-receiver 36 located at the lower end of the flexible pipe 23.

The transmitter 36a (FIG. 3) is of a type transmitting a very narrow directional beam of ultrasonic signals and is driven in rotation at substantially constant speed around the axis of the pipe 23 by means of an electric motor 37 through a reduction gear 38, in such manner as to sweep the space all around the lower end of the pipe 23 with the beam.

A gyroscopic device 39 is also secured to the lower end of the pipe 23 for locating at any moment the direction of the ultrasonic beam. This location is performed by coupling the rotary part of the transmitter with the transmitter element of a synchromechanism of the Selsyn type whose stator is connected to the gyroscope 39. Under these conditions, this transmitter element transmit at any moment the directional position of the ultrasonic beam to the ship in the form of an electrical signal representing the difference between the directional position of the ultrasonic transmitter 36a and the reference direction indicated by the gyroscope 39 (direction of the north).

This electrical signal is amplified by the preamplifier 42 before being transmitted to the receiving element 44 of the synchromechanism or Selsyn located on the ship 14, the transmission occuring through the teletransmission conductor 43 which is advantageously incorporated in the flexible pipe 23.

The output signal from 44 is applied to a radar indicator 45 whose screen 450 is thus swept, as indicated by the arrow at the speed of rotation of the ultrasonic transmitter 36a, the horizontal reference direction provided by the gyroscope being displayed on the screen 45a.

The screen 45a thus displaying the position of the lower end of the pipe 23 relative to the responders R,, R, and R by the respective distances OR,, OR, and OR,, it will be possible to position just above the valve 13 by manual or automatic control of one or more fluid jets escaping through the orifices 32 to 35.

it will then be sufficient to unreel an additional length of the pipe 23 from the ship 14 to achieve the insertion of this pipe into the underwater tank by causing the floating piston which seals the valve to slide downwards. The pumping condition is the created.

After draining the tank it is sufficient to raise the duct 23, the ship then sailing back to the discharging harbor.

The invention is equally applicable in the case of one or more underwater tanks equipped in known manner with submerged pumps and submerged draining pipes provided with valves and automatic safety devices as specified in the introductory part of this specification, the device according to the invention then being used for draining of the tank or tanks in case of defective operation of the pump incorporated in a tank, of the valves or devices automatic equipping the tank or the submerged draining pipes.

The device according to the invention may equally be used to raise a defective item of equipment by means of the pipe 23, in the case in which this item may be raised by simple traction.

On the ship 14 the electrical connection between the conductors incorporated in the flexible pipe 23 and the source of electrical power, the measuring devices or the devices for remote control, may be achieved in known manner, through conducting rings keyed to the shaft of the reel 24 and electrically insulated from one another, on which rub conducting segments or brushes connected with the different electric or electronic devices on the ship.

We claim:

1. A device for draining to a loading installation fluids contained in at least one submerged tank provided with coupling means, including at least one flexible pipe which can be submerged from said loading installation, said flexible pipe being associated with at least one line for transmitting power from said loading installation and being provided, substantially at its lower end, with means for detachably connecting said pipe to the coupling means on said tank, means for suction and delivery of said fluid being located substantially at the lower end of said flexible pipe and actuated by the power transmitted through said line, said suction and delivery means penetrating into the tank upon engagement of said connecting means with said coupling means, thereby providing for suction and delivery of the fiuid from said tank to said loading installation through said flexible pipe, said device comprising in combination first location means associated with said tank for positioning said loading installation substantially above said tank and second locating means including stationary locating means on said tank, associated with said coupling element, and sensing means located substantially at the lower end of said flexible pipe and electrically connected to said loading installation for determining the distance between said connecting means of said flexible pipe and said coupling means on said tank.

2. Device according to claim 1, wherein said line for transmitting power is an electrical power line.

3. Device according to the claim 1, wherein said line for transmitting power is a hydraulic line.

4. Device according to claim 1, wherein propulsion means are provided at the lower end of said flexible pipe.

5. Device according to claim 14 wherein the lower end of said pipe is provided with propulsion means actuated by electrical power transmitted through conductors of said power line from said loading installation.

6. Device according to claim 4, wherein said propulsion means are of the fluid jet type.

7. Device according to claim 1, wherein said flexible pipe is provided at its lower end with locating means for determining the distance separating said end from coupling means on said tank.

8. Device according to claim 7, wherein said locating means are constituted by the cooperation of an acoustic transmitterreceiver device and at least three responders of acoustic signals said responders having fixed locations with respect to said tank, said transmitter-receiver device including means for transmitting an ultrasonic beam rotating about the axis of said flexible pipe.

9. Device according to claim 1, wherein said means for coupling said pipe to the tank comprises a valve of the flap type.

10. Device according to claim I, wherein said means for coupling said pipe to the tank comprises a valve of the type having movable jaws providing for sealing during the lowering of the lower end of the pipe into the tank and for automatic total closure after withdrawal of said pipe from said tank.

11. Device according to claim 1, wherein said means for coupling said pipe to said tank comprises a valve of the floating piston type, adapted to receive the lower end of flexible pipe, whilst establishing a communication between this latter and the inside of the tank, by downward displacement of said floating piston.

12. Device for draining a submerged tank which belongs to a set of submerged tanks, comprising in combination a mobile installation provided with a dynamic positioning device employing means for locating the position of said installation relative to a system of rangingunits, wherein each submerged tank is located by means of its coordinates related to said system of ranging units, means for determining the differences between the corresponding coordinates of said submerged tank and said installation, said locating means cooperating with said dynamic positioning device to reduce the said differences, a flexible draining pipe, means for lowering said pipe from said mobile installation, said draining pipe being at its lower end provided with means for connection with a comple mentary coupling element of said tank, means for displacing said lower end of said pipe, suction and delivery means located substantially at the lower end of said flexible pipe and supplied with power from said mobile installation through at least one power line associated with said flexible pipe, meansfor determining the distance separating said connection means of said pipe from said coupling means of said tank and propul sion means, provided substantially at the lower end of' said flexible pipe, for reducing said distance substantially to zero.

13. Method for draining a submerged tank which belongs to a set submerged tanks, from a mobile installation provided with a dynamic positioning device which includes means for locating the position of said installation with respect to a system of ranging units, comprising the following successive steps:

a. locating the respective positions of said submerged tank and of said mobile installation in the form of coordinates relative to said system of ranging units,

b. measuring the difierences between the corresponding coordinates of said tank and of said mobile installation in said system of ranging units and actuating said dynamic positioning system to reduce said differences,

c. lowering from said mobile installation a flexible draining pipe of which the lower end is provided with an element for connection to a complementary coupling element on said submerged tank and which is provided with propul- 

1. A device for draining to a loading installation fluids contained in at least one submerged tank provided with coupling means, including at least one flexible pipe which can be submerged from said loading installation, said flexible pipe being associated with at least one line for transmitting power from said loading installation and being provided, substantially at its lower end, with means for detachably connecting said pipe to the coupling means on said tank, means for suction and delivery of said fluid being located substantially at the lower end of said flexible pipe and actuated by the power transmitted through said line, said suction and delivery means penetrating into the tank upon engagement of said connecting means with said coupling means, thereby providing for suction and delivery of the fluid from said tank to said loading installation through said flexible pipe, said device comprising in combination first location means associated with said tank for positioning said loading installation substantially above said tank and second locating means including stationary locating means on said tank, associated with said coupling element, and sensing means located substantially at the lower end of said flexible pipe and electrically connected to said loading installation for determining the distance between said connecting means of said flexible pipe and said coupling means on said tank.
 2. Device according to claim 1, wherein said line for transmitting power is an electrical power line.
 3. Device according to the claim 1, wherein said line for transmitting power is a hydraulic line.
 4. Device according to claim 1, wherein propulsion means are provided at the lower end of said flexible pipe.
 5. Device according to claim 14 wherein the lower end of said pipe is provided with propulsion means actuated by electrical power transmitted through conductors of said power line from said loading installation.
 6. Device according to claim 4, wherein said propulsion means are of the fluid jet type.
 7. Device according to claim 1, wherein said flexible pipe is provided at its lower end with locating means for determining the distance separating said end from coupling means on said tank.
 8. Device according to claim 7, wherein said locating means are constituted by the cooperation of an acoustic transmitter-receiver device and at least three responders of acoustic signals said responders having fixed locations with respect to said tank, said transmitter-receiver device including means for transmitting an ultrasonic beam rotating about the axis of said flexible pipe.
 9. Device according to claim 1, wherein said means for coupling said pipe to the tank comprises a valve of the flap type.
 10. Device according to claim 1, wherein said means for coupling said pipe to the tank comprises a valve of the type having movable jaws providing for sealing during the lowering of the lower end of the pipe into the tank and for automatic total closure after withdrawal of said pipe from said tank.
 11. Device according to claim 1, wherein said means for coupling said pipe to said tank comprises a valve of the floating piston type, adapted to receive the lower end of flexible pipe, whilst establishing a communication between this latter and the inside of the tank, by downward displacement of said floating piston.
 12. Device for draining a submerged tank which belongs to a set of submerged tanks, comprising in combination a mobile installation provided with a dynamic positioning device employing means for locating the position of said installation relative to a system of ranging units, wherein each submerged tank is located by means of its coordinates related to said system of ranging units, means for determining the differences between the corresponding coordinates of said submerged tank and said installation, said locating means cooperating with said dynamic positioning device to reduce the said differences, a flexible draining pipe, means for lowering said pipe from said mobile installation, said draining pipe being at its lower end provided with means for connection with a complementary coupling element of said tank, means for displacing said lower end of said pipe, suction and delivery means located substantially at the lower end of said flexible pipe and supplied with power from said mobile installation through at least one power line associated with said flexible pipe, means for determining the distance separating said connection means of said pipe from said coupling means of said tank and propulsion means, provided substantially at the lower end of said flexible pipe, for reducing said distance substantially to zero.
 13. Method for draining a submerged tank which belongs to a set submerged tanks, from a mobile installation provided with a dynamic positioning device which includes means for locating the position of said installation with respect to a system of ranging units, comprising the following successive steps: a. locating the respective positions of said submerged tank and of said mobile installation in the form of coordinates relative to said system of ranging units, b. measuring the differences between the corresponding coordinates of said tank and of said mobile installation in said system of ranging units and actuating said dynamic positioning system to reduce said differences, c. lowering from said mobile installation a flexible draining pipe of which the lower end is provided with an element for connection to a complementary coupling element on said submerged tank and which is provided with propulsion means for displacing said lower end in the water, said flexible pipe being provided, substantially at its lower end, with suction and delivery means supplied with power from said mobile installation through at least one power line associated with said flexible pipe, d. determining the distance between said connection element and said coupling element, e. actuating said displacing means to reduce said distance to zero, f. connecting said connection element and said coupling element and, g. supplying power to said suction and delivery means through said power line, to drain said submerged tank. 